Chair base

ABSTRACT

An anti-tipping chair base has a central support member with a generally upright axis, and a plurality of arms that extend generally radially outwardly from the axis and each of which is provided with a caster. An outer end portion of the arm has a shape that curves downwardly around the caster to an end edge outwardly of the caster. As seen in plan, the outer end portion of the arm has side edges that diverge in a direction towards the end edge and between which the end edge extends generally normal to the radial direction of the arm. The end portions of the arm comprise support elements that contact a surface on which the base is disposed in the event that the base tips in use.

FIELD OF THE INVENTION

[0001] The present invention concerns a so-called “anti-tipping” chair base, for example for an office chair.

BACKGROUND OF THE INVENTION

[0002] DE-GM 73 44 658 discloses a chair base having a plurality of arms which extend radially outwardly from a central support column, and each of which has a caster at its outer end. Each caster is surrounded by a bell whose outer contour has one or several lower edges that function as support elements if the chair tips. A disadvantage here is that the respective lower edges of the supporting elements, in the normal position of the chair base, are low to the ground and support in an undefined position when the chair tips.

SUMMARY OF THE INVENTION

[0003] An object of the invention is to improve the effectiveness of the chair base in the tipped position.

[0004] According to the invention, there is provided an anti-tipping chair base comprising a central support element having a generally upright axis and a plurality of arms that extends generally radially outwardly from the axis and each of which is provided with a caster adjacent an outer end portion of the arm. The outer end portion of each arm has a shape that curves downwardly around the caster to an end edge outwardly of the caster and that is defined as seen in plan by side edges that diverge in a direction towards the end edge and between which the end edge extends generally normal to the radial direction of the arm. The end portions of the respective arms comprise support elements for contact with a surface on which the base is disposed in the event that the base tips in use.

[0005] One embodiment of the invention envisions a support element that is fork-shaped with the two fork ends connected by an essentially horizontal connecting bar. In this way, each support element forms with an adjacent arm, a defined resting point in any given tipped position of the chair, which means that the chair is securely supported on the floor in any tipped position of the chair, even when the casters are turned inwards.

[0006] The connecting bar may be arcuate in a direction outwardly from the centre of the base. This protects the user of the chair against accidentally trapping a foot between the two fork ends.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which illustrate a particular preferred embodiment of the invention by way of example, and in which:

[0008]FIG. 1 is a perspective view from above of a five-arm chair base in accordance with the invention;

[0009]FIG. 2 is a plan view corresponding to FIG. 1;

[0010]FIG. 3 is a plan view of an outer end portion of one of the arms with the caster turned inwardly;

[0011]FIG. 4 is a side elevational view corresponding to FIG. 3;

[0012]FIG. 5 is a front elevational view corresponding to FIG. 3;

[0013]FIG. 6 is a front elevational view of the base showing one caster turned inwardly and one caster turned outwardly; and,

[0014]FIG. 7 is view similar to FIG. 6, showing the base in a tipped position.

DESCRIPTION OF PREFERRED EMBODIMENT

[0015] The anti-tipping chair base in accordance with the invention includes a central support element 2 having a generally upright axis A-A and a plurality of arms 3 that extend generally radially outwardly from axis A-A. Each arm is provided with a caster 4 adjacent an outer end portion 3 a of the arm.

[0016] As best seen in FIGS. 4, 6 and 7, the outer end portion 3 a of each arm has a shape that curves downwardly around the caster to an end edge 3 b outwardly of the caster. The shape of the outer end portion as seen in plan is defined by side edges 3 c that diverge in a direction towards the end edge 3 b and between which the end edge 3 b extends generally normal to the radial direction of the arm. The end portions 3 a of the respective arms accordingly provide support elements for contact with a surface on which the base is disposed in the event that the base tips in use.

[0017] As will be described in more detail below, the drawings show an embodiment of the invention in which the outer end portion 3 a (supporting element) of each arm is generally fork-shaped with a bar that extends between the outer ends of the limbs of the fork. However, this fork shape is not essential to the invention. In another embodiment, the outer end portion 3 a of each arm could be of plain (imperforate) generally triangular shape.

[0018] Referring now more specifically to the drawings, the central support element 2 of the base 1 is designed to receive a support column for the seat and back assembly of the chair (not shown); typically, element 2 will be of hollow cylindrical form.

[0019] The chair base 1, element 2 and arms 3 can be made of metal or plastic and may be made in one piece. Casters 4 have conventional double-roll wheels which turn on respective horizontal axes B-B (FIG. 2). Each caster also has a pin 5 which is set on a vertical axis 6 of the respective arm 3, so that the caster can turn about axis 6.

[0020] The supporting element (3 a) of each arm 3 may be made in one piece with the arm 3 or separately and may be made of metal or plastic. In this embodiment, the supporting element 3 a is fork-shaped and the two fork limbs diverge at about 60° to form two horizontally spaced support points 9, 10 (FIGS. 3, 4 and 5). Points 9, 10 may be located at a distance d (FIG. 4) of 3 to 10 mm from the floor when the center axis A-A of the chair base 1 is in a vertical position. The support points 9, 10 of two neighbouring, opposed fork ends 8 of adjacent arms 3 form a virtual standing surface that provides the required stability of the base of the chair (in particular an office chair) in the tilted position of the chair base 1. The two forked ends 8 are connected by a horizontal connecting bar 11 that is outwardly arcuate in relation to the centre axis A-A of the chair base 1.

[0021] A chair base 1 according to the invention having fork-shaped support elements 3 a meets the German Industrial Standard for the stability of rotatable office chairs (DIN 445/52). The measure of stability is determined as the smallest distance between a line connecting two neighbouring support points 9, 10 to the rotary axis A-A of the chair.

[0022] Support points 9, 10 are those points of movable or rigid parts of the chair that are always in contact with the floor. When using casters the caster position which is least favourable to stability must be the starting point. Apart from the measure of stability required here, stability is increased by the fork-shaped supporting elements 3 a of the chair base 1, because the bearing structure of each arm is extended somewhat past the relevant caster 4. In this case, the fork ends 8 of the supporting elements 7 are spaced 3 to 10 mm above the floor. In an extreme seated position with the casters 4 (FIG. 7) turned inwardly towards the central axis A-A of the base 1, the base 1 and therefore the office chair are prevented from tipping.

[0023] The support elements 3 a can be made of the same material as the arm 3 and may be formed in one piece from plastic, aluminum or steel. The support elements 3 a can also be separate components made from aluminum, steel or plastic and attached to the main part of the arm 3 on which the caster 4 is mounted.

[0024] It will of course be appreciated that the preceding description relates to a particular preferred embodiment of the invention only and that many modifications are possible within the broad scope of the invention. Some of those modifications have been indicated previously and others will be apparent to a person skilled in the art. Clearly, the overall form of the base shown in the drawings is an example only. The anti-tipping feature of the invention may be applied to bases of other configurations (different numbers and shapes of arms and different types of casters). 

I claim:
 1. An anti-tipping chair base comprising a central support member having a generally upright axis, and a plurality of arms that extend generally radially outwardly from said axis and each of which is provided with a caster adjacent an outer end portion of the arm, wherein said outer end portion of each arm has a shape that curves downwardly around the caster to an end edge outwardly of the caster and that is defined as seen in plan by side edges that diverge in a direction towards said end edge and between which said end edge extends generally normal to the radial direction of the arm, said end portions of the respective arms comprising support elements for contact with a surface on which the base is disposed in the event that said base tips in use.
 2. A chair base as claimed in claim 1, wherein the outer end portion of each arm comprising a said supporting element is fork-shaped, comprising a pair of divergent limbs and a transverse bar connecting outer ends of said limbs.
 3. A chair base according to claim 2, wherein the connecting bar is arcuate in a direction outwardly from the axis of the central support member.
 4. A base according to any one of the preceding claims, wherein the outer end portion of each arm comprising said support element is a component separate from the remainder of the arm. 